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Virtual NUMA (vNUMA) and CPU Hot-Add support in vSphere 8

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While looking for something in the vSphere 8.0 API Reference, I stumbled onto a new VM configuration setting in vSphere 8 called exposeVnumaOnCpuHotadd which looks quite interesting and has the following description:

Capability to expose virtual NUMA when CPU hotadd is enabled. If set to true, ESXi will consider exposing virtual NUMA to the VM when CPU hotadd is enabled. If set to false, ESXi will enforce the VM to have single virtual NUMA node when CPU hotadd is enabled. If unset, the VM continue to follow the behavior in last poweron.

This actually reminded me of question that we got during one of our vSphere 8 Meet the Experts (MTE) sessions at VMware Explore Barcelona and whether there were any new enhancements to vNUMA when CPU hot-add is enabled, which I was not aware of any at the time. The vNUMA and CPU Hot-Add issue is detailed in this blog post by no other than my buddy Frank Denneman and here is a quick summary of the issue:

CPU Hot-Add is not compatible with vNUMA, if hot-add is enabled the virtual NUMA topology is not exposed to the guest OS and this may impact application performance.

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Quick Tip - Changes to building custom ESXi images in vSphere 8

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Historically, when a new version of ESXi is released, customers will use vSphere Image Builder either through the vSphere Image Builder UI or PowerCLI Image Builder cmdlets to create a custom ESXi image to include additional drivers such as the USB Network Native Driver for ESXi Fling.

Note: The current version of the USB Network Native Driver for ESXi Fling is not compatible with ESXi 8.0 and a new version of the driver will be needed. There is currently no ETA on when a new version will be available.

Typically, customers will use their existing vCenter Server deployment, which is usually running an older version to create their new custom ESXi image. This means you are importing a newer ESXi release into your vCenter Server or in the case of the PowerCLI Image Builder cmdlets, you are using an older release of PowerCLI. While this may have worked with previous releases, the assumption that vSphere Image Builder is "forward" compatible with future releases of ESXi is actually an incorrect assumption that many have made, including myself.

I bring this up because in vSphere 8, there have been changes in ESXi where this incompatibility will be observed when attempting to create a custom ESXi 8.0 image using a non-compatible vCenter Server or a PowerCLI release.

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Using vSphere Lifecycle Manager (vLCM) to remediate Nested ESXi host with CPU on the host is not supported 

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If you are running a Nested ESXi VM on top of a physical ESXi host that does not have a supported CPU and you are using vSphere Lifecycle Manager (vLCM), the pre-check and/or remediation will fail due to the following error:

The CPU on the host is not supported by this image


The solution is actually quite simple and is similiar to what you had to do for your physical ESXi host by adding the ESXi kernel boot option allowLegacyCPU=true to successfully boot and install ESXi as recently explained in this blog post. To emulate this setup, I am using my trusty 2011 Apple Mac Mini which is running ESXi 8.0 with the kernel boot option and it is then running a Nested ESXi 7.0 Update 3g VM.

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